Talk:7-Dehydrocholesterol

7-Dehydrocholesterol conversion to pre-vitamin D3
How does the concentration of 7-Dehydrocholesterol in human skin vary with age etc?

How fast does the conversion reaction to pre-vitamin D3 take place, when exposed to UVB? Minutes? Seconds? Faster? How brief of an exposure of human skin to UVB is succifient for the process to take place?

Is the conversion reaction proportional to UVB exposure, over a wide range? Or is there perhaps a threshold of UVB that must be exceeded for the reaction to take place? And is there an upper limit of UVB intensity, beyond which reaction efficiency is reduced?

How does all of this vary in different species?

What is the logic or evolutionary "reason" for requiring external UVB to produce the required Vit D? Do any species somehow synthesize Vit D without depending on external UVB? -71.174.180.139 (talk) 01:49, 4 June 2010 (UTC)

"7-dehydrocholesterol in the skin absorbs UVB photons with energies between 290 and 315 nm in its 5,7-diene region, forming previtamin D3. [1] This reaction is purely dependent on light, and takes place in all animals but is particularly important in vertebrates. If 7-DHC is placed in vitro (in quartz tubes), the reaction takes place in the same way. It is not dependent on enzymes or cells at all. [2][3] If this previtamin D3 remains in the skin, and is further exposed to light, it breaks down into inert bioproducts, lumisterol and tachysterol. [1] No more than 15% of 7-DHC in the skin can be transformed to previtamin D3 in humans, no matter how long the exposure to sunlight. [4] This may be the maximum in all systems as it is the maximum in vitro [2] [3] and the maximum in surgically obtained human skin [7]. This is a useful regulatory device, making it impossible for an animal to produce too much previtamin D3. If the stores of previtamin D3 are completely depleted, lumisterol and tachysterol then become able to be photo-isomerized to previtamin D3, so these compounds are useful storage devices. [5]" http://www.anapsid.org/uvbanne.html 1999 Anne Marsden

This source has additional interesting details. -71.174.180.139 (talk) 03:28, 4 June 2010 (UTC)

Article appears biased towards the substance's role in humans.
Prompted by this article Not Exactly Rocket Science (Sept 2012), I've added a sentence on the role of the substance in insects. I was actually looking for some background on this, but only found the current description of the substance in humans, and its relation to Vitamin D3.

Ed Yong writes: ''The Neverland gene makes a protein of the same name, which converts cholesterol into 7-dehydrocholesterol. This chemical reaction is the first of many that leads to ecdysone – a hormone that all insects need to transform from a larva into an adult. Most species make their own ecdysone but D.pachea is ill-equipped.''

Lang, Murat, Clark, Gouppil, Blais, Matzkin, Guittard, Yoshiyama-Yanagawa, Kataoka, Niwa, Lafont, Dauphin-Villemant & Orgogozo. 2012. Mutations in the neverland Gene Turned Drosophila pachea into an Obligate Specialist Species. Science

doi link, not yet verified

Henk Langeveld (talk) 14:51, 28 September 2012 (UTC)

This article talks primarily of vitamin D generation. It has little on the actual 7-Dehydrocholesterol beyond it is found in the skin. Where does it come from? Does the liver generate it? Or the skin (if so, the article should specifically state that). What is it made from? Does it do anything else? As a non bio-chemist, I was looking for more info on 7-Dehydrocholesterol, not vitamin D. Olan7allen (talk) 19:26, 29 June 2014 (UTC)

Capitalization
Shouldn't the substance's name be written in all lowercase, "7- d ehydrocholesterol"? Petr Matas 21:35, 7 September 2016 (UTC)

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That's well & good, buy where does it come from?
Presumably not just there since birth. ˥ Ǝ Ʉ H Ɔ I Ɯ (talk) 05:37, 10 September 2018 (UTC)